As disclosed in Japanese Patent Unexamined Publication No. 61-132466, there has been known a reaction controlling apparatus in which a first fixed throttle is disposed in an oil path between an exhaust port of a pump and a power steering valve. A second fixed throttle and a variable throttle with its opening controlled in accordance with vehicle speed, steering angle or the like, are provided in series in another oil path connecting the upstream of the first fixed throttle with a tank or a return path, so that regulated oil pressure in an intermediate portion between the second fixed throttle and the variable throttle is led to a hydraulic reaction chamber.
As disclosed in Japanese Unexamined Patent Publication No. 52-140129, there has been known another reaction controlling apparatus in which two variable throttles connected to a solenoid actuated by a signal from a vehicle speed sensor are disposed in series in an oil branch path that branches off from an oil path between an exhaust port of a pump and a power steering valve and which is connected to a tank so as to lead oil pressure to a hydraulic reaction chamber, whereby regulated oil pressure at an intermediate portion between the two throttles is led to the hydraulic reaction chamber.
Further, as disclosed in Japanese Unexamined Patent Publication No. 55-76764, there has been known a further reaction controlling apparatus in which two variable throttles linked in series by a coupling element actuated manually or by an output quantity of a tachometer are disposed in an oil branch path which is branched off from an oil path between an exhaust port of a pump and a power steering valve and which is connected to a tank so as to lead oil pressure to a hydraulic reaction chamber. With this device, regulated oil pressure at an intermediate portion between the two throttles is led to the hydraulic reaction chamber.
In the hydraulic reaction controlling apparatus disclosed in Japanese Unexamined Patent Publication No. 61-132466, however, there has been a problem in that since the apparatus is arranged such that the reaction oil pressure to be regulated is obtained by the variable and fixed throttles disposed in series, the reaction pressure to be regulated depends on the size of the fixed throttle of a stepping valve during high speed running of a vehicle when the variable throttle is opened. The reaction pressure cannot be sufficiently raised to accommodate the increase of return oil passing there, so that sufficient reaction pressure cannot be obtained.
Further, in the hydraulic reaction controlling apparatus disclosed in Japanese Unexamined Patent Publication No. 55-76764, there has been a problem in that although the apparatus is operated manually or by an output quantity of a tachometer, smooth pressure control cannot be performed since the two throttles change at the same time in the manner of the case described above.
In view of the foregoing problems in the prior art, it is an object of the present invention to provide a hydraulic reaction controlling apparatus that is arranged such that a fixed throttle is provided between two variable throttles disposed in series.
Another object of the present invention is a hydraulic reaction controlling apparatus wherein the return flow is controlled to raise the reaction pressure to a large degree so that sufficient reaction can be obtained during high speed and a smooth pressure characteristic can be obtained during moderate vehicle speed.
A further object of the present invention is a hydraulic reaction controlling apparatus wherein the throttles are arranged on the same shaft so that the apparatus can be made simple in structure.